Our verdict
Not really a dog walk — it's a protected geological site without public access, and visits are normally arranged through Beaminster Museum rather than dropped into on a walk. Included here for completeness; don't plan a trip around it.
England's smallest National Nature Reserve, a disused quarry a couple of miles west of Beaminster within Horn Park Business Centre. It preserves a bed of Middle Jurassic rock roughly 170 million years old and is a world-reference site for ammonite fossils.